Head and shoulder patterns occur very often and they will conitnue to form and follow through because it is just how the supply and demand shapes the chart pattern. There are people in there playing the pattern as a 'system'.
Breakouts occur all of the time and there are people playing those breakouts using a system.
Now, take some specific indicator or numbers based system or any kind of exact measured type of value and when these exact values line up have enough people trading this to the point that it actually affects supply / demand and yes it can change the results of a 'system'.
Try telling 10 people to trade with 1000 shares long when a 12,26,9 MACD closes above the zero line on a stock that trades 100,000 shares a day and I guarantee you that the sytem itself will not work after time and of course with more and more people knowing about it.
Breakouts occur all of the time and there are people playing those breakouts using a system.
Now, take some specific indicator or numbers based system or any kind of exact measured type of value and when these exact values line up have enough people trading this to the point that it actually affects supply / demand and yes it can change the results of a 'system'.
Try telling 10 people to trade with 1000 shares long when a 12,26,9 MACD closes above the zero line on a stock that trades 100,000 shares a day and I guarantee you that the sytem itself will not work after time and of course with more and more people knowing about it.